Coordinating two arms for function PROJECT SUMMARY: Inability to use the weaker arm in functional activities accounts for over 50% of reduction in the quality of life after stroke. Most functional activities of daily living involve a coordinated use of both hands to accomplish different task goals. Despite the prevalence of bimanual actions in daily life, much of post-stroke arm rehabilitation research is focused on the assessment and treatment of the weaker arm, with little focus on how bimanual actions are affected. An underlying assumption, that has not been tested rigorously, is that unimanual performance deficits primarily account for impairments in coordination of bimanual actions. While deficits in the arm contralateral to stroke are discernible, critical motor control deficits in the ipsilateral arm have also been reported. In addition, many task goals require higher-order motor plans that engage interhemispheric connections to control spatiotemporal interaction between the two arms. Further, there are multitude of ways in which two hands interact in time and space to accomplish different tasks, leading to distinct classes of bimanual coordination. Our long-term goal is to identify the motor, cognitive and neural contributors to bimanual actions in patients with stroke so that treatment strategies can be focused on the most crucial determinants. The proposed study will determine the relative impairments in different classes of bimanual actions after stroke and the degree to which the unimanual performance deficits predict bimanual impairment. The specific aims of this project are to: 1) identify abnormalities in bimanual coordination in patients with stroke for distinct classes of functional tasks compared to age-matched controls, (2) determine the relationship of sensorimotor deficits and unimanual performance of the paretic hand with bimanual coordination measures in patients with stroke. The approach is particularly innovative because we use combined kinematic and kinetic data to determine how control and coordination of distinct classes of bimanual actions is affected. We hypothesize that patients with stroke will demonstrate task-dependent impairments in coordinating their two arms compared to control participants. Further, unimanual performance deficits may predict coordination insufficiencies for classes of bimanual actions that involve each hand pursuing an independent goal than those that involve both hands contributing to a common goal. The proposed project is significant in that it provides an important first step in determining the contribution of unimanual impairments in bimanual coordination during distinct classes of bilateral actions. For those class of bimanual actions in which unimanual performance deficits significantly account for bimanual coordination deficits, future experiments will determine the effects of intense unimanual practice on bimanual coordination. If we observe that unimanual impairments do not predict coordination in certain class of bimanual actions, future research will focus on determining the cognitive, perceptual and neural factors that determine bimanual coordination for these actions.